Cathepsin-K inhibition is a novel approach to osteoporosis treatment and Merck’s odanacatib is leading the way in this new class of drugs. It is currently in phase III development, with 16,716 subjects enrolled (NCT00529373).

Cathepsins are lysosomal proteases. Cathepsin K (Cat-K) is a cysteine protease that plays an important role in the function of osteoclasts (the cells responsible for bone destruction). Cat-K acts to degrade bone collagen. By inhibiting it, the removal of bone matrix proteins by osteoclasts is reduced.

However, Cat-K inhibitors such as odanacatib do not kill off the osteoclast, but allow it to still produce chemokines and growth factors such as WNT that are responsible for the effective function of osteoblasts (the cells responsible for bone formation).

The net result is that Cat-K inhibitors reduce bone resorption.

Phase II clinical trial results for odanacatib presented at the American Society of Bone and Mineral Research (ASBMR) annual meeting last year (abstract #1247), showed an increase in spine and hip bone mineral density (BMD) after four years of follow-up, suggesting that odanacatib use leads to increased bone strength. As reported by Merck in their press release:

In postmenopausal women who received odanacatib 50 mg weekly for four years (N=13), an increase in BMD of 2.8 percent at the lumbar, and 2.7 percent at the hip were demonstrated between years three and four of treatment. Over four years of treatment, these women had increases in lumbar spine (10.7 percent) and hip (8.3 percent) BMD from baseline.

If you are looking for further information on the science, the February 2011 issue of “The Journal of Bone and Mineral Research” has several papers on odanacatib, osteocytes and cathepsin K inhibitors.

Merck has 16,716 subjects enrolled in their phase III trial for odanacatib, and July 2012 is indicated as the date when data will be available for the primary end-point of reduction in fracture risk over the three year treatment period. We can expect the phase III results shortly after that, and if positive, an FDA approval could be expected in 2013.

The development of odanacatib by Merck is clearly a strategy to combat generic alendronate, which has eroded Merck’s market share and profits for Fosamax. Both odanacatib and generic alendronate, are once weekly doses. The timeline for a product launch for odanacatib appears to be in the late 2013/2014 period, and I am sure further clarity on this will appear from Merck nearer the time.

The challenge for odanacatib is that by 2015, analysts estimate that Amgen’s RANKL inhibitor denosumab will be a blockbuster (more than $1 billion in sales) and sales of parathyroid hormone analogues will have tripled to $1.4 billion.

Although the market opportunity in osteoporosis is likely to grow given the aging population around the world, it remains to be seen how the cost/benefit of odanacatib will stack up against the competition, and whether Merck can capitalize on this.

The news, reported by Bloomberg, last week that generic companies may be subject to stricter FDA standards in order to show therapeutic equivalence is good news for the biotech industry and consumers.

Generic companies have a pretty easy ride in obtaining product approval, and I’ve long been convinced that the formulation of a brand, and what makes it work can include the so called inactive ingredients and how it is put together. I know of many people who have experienced side effects with generics that they don’t have with the branded product.

For this reason, branded generics from the original manufacturer have the ability to retain some market share in the face of generic competition. Sandoz, the generic arm of Novartis uses this strategy to good effect with many mature products. However, if companies instead want to try and maintain a premium priced brand and not adapt to the entry of generics, then they will find their market share erodes extremely fast. Not only is brand market erosion fast with generic drugs, but with biosimilars too.

As reported by Reuters, sales of generic enoxaparin sodium injection, Momenta’s copy of Sanofi’s anti-thrombotic, low molecular weight, heparin sold as “Lovenox” were $292million in the third quarter of 2010. Sandoz markets enoxaparin on behalf of Momenta. They launched the product on July 23, and achieved $292 million of sales in 69 days. With annual sales forecast to be over $1billion, the biosimilar will be a blockbuster and make a significant dent in the $2.9 billion sales of Lovenox in 2009.

The Boston Business Journal reports that Sandoz/Momenta have captured 60% market share already, which is not good news for Sanofi-Aventis and may explain their desire to make acquisitions such as Genzyme to make up for this loss.

Biosimilars that are fully substitutable for the original product, look likely to erode brands extremely fast. Momenta’s success is good for the biotechnology industry and highlights the future market opportunity from development of biosimilars.